1. Field of the Invention
The present invention relates generally to pistons, and particularly relates to a plastic accumulator piston constructed from separate components so as to facilitate its manufacture.
2. Description of Prior Developments
An automotive transmission often includes one or more pumps for supplying pressurized hydraulic liquid to clutch actuators located within the transmission. Such transmission actuators perform somewhat better if the pressurized liquid is free from pressure spikes or surges. In order to remove such pressure spikes from the pressurized liquid, the principal liquid passage containing the pressurized liquid is often connected to an accumulator.
The accumulator can include a cylinder containing a floating piston, and some means to bias the piston in a direction opposing the pressure surge. Each pressure spike deflects the piston so as to slightly increase the cylinder volume in communication with the flow passage. The increased cylinder volume dissipates the pressure surge, whereby the liquid is relatively free from pressure pulses or spikes after its passage beyond the accumulator.
In one particular known accumulator construction, the accumulator piston and associated cylinder are of a radially stepped design such that the piston has a first annular sealing element sliding on the cylindrical surface of a larger diameter chamber and a second sealing element sliding on the cylindrical surface of a smaller diameter chamber. A pressurized control liquid is supplied to an annular space surrounding the piston between the two sealing elements.
Due to the area differences between the two chambers, the pressurized control liquid exerts an axial biasing force on the piston, whereby the piston acts as a movable, resilient absorption device for pressure surges in the associated flow passage.
In the described accumulator design, the piston is of cast aluminum construction and each sealing element is an O-ring. It has been found that the O-ring sealing elements tend to fail after a relatively short period of use. Seal failure may be due to the fact that the piston is subject to cyclical motion back and forth in the stepped cylinder.
Turning and flexing of the seal element materials around the cylinder contact points tend to product fatigue failure of the seal element materials.